UPDATE!!
Bri seems to be 100% better!
She was back to her normal self after the first day of Corid!
She and the entire flock have been on Corid and were wormed with Valbazen! The whole flock is together, everyone is eating and drinking, and our egg production has increased!
Almost done with the Corid treatment and worming again after 10 days from the first dose.
Also helps that the weather is back below 100!
Lastly, I was able to find a bird clinic to do the fecal test, but I called about 10 vets to ask if they would do it for me and they said no, so I guess the regular vets around here won't test chicken poop! If anyone in the Austin/Round Rock area ever needs a bird vet there are 2 in the area:
Wells Branch Pet and Bird Clinic (where I went but wouldn't necessarily recommend)
Research Pet and Bird Hospital (less convenient and more expensive, but I have nothing but good reviews for this vet)
Thanks to everyone who helped me and my girls! Especially KikisGirls!